There's definitely something about the shape of his legs that seems not anatomically correct but the proportions don't seem that bad.
Another issue is that the pant legs are the same average thickness from the thigh to the cuff, they seem to vary in thickness, and they seem to heavily bow out at the shins and then get sucked back in at the ankles. Remember, while a tube of cloth may wrinkle and drape over his leg, it should not actually change in overall diameter. This means that a huge bugle on one side would be met with the opposite on all other sides, and if it was compressed on one axis, it will expand on the perpendicular axis.
His left pant leg also seems to cut out an area where I would expect his calf muscle to be. On the right pant leg, there is a bump that is higher at the top than at the bottom- which may be physically possible with very stiff pants, it is highly unusual and unlikely.
I think a good place to start would be to eliminate the odd bumps and flares in the cuffs of his trousers. With that done you may try tapering them slightly. However, after you do straighten out the pant legs a little, we can take another look at the proportions, and then you can add some back in.
edit: There also might be something going on in his pelvis area, and in the crotch of his pants. His upper thighs feel bound or something like his pants are riding too low, but I can't put my finger on it. I think the joints are not correctly rigged, and that his thighs should be thicker higher up or something. His actual hip joints feel pushed downwards, I think.